1. Field
The present invention relates generally to communication systems, and more specifically, to a method and apparatus for communication in a wireless communication system employing differing transmission protocols.
2. Background
Wireless communication technologies have seen explosive growth over the past few years. This growth has been primarily fueled by wireless services providing freedom of movement to the communicating public as opposed to being “tethered” to a hard-wired communication system. It has also been fueled by the increasing quality and speed of voice and data communications over the wireless medium, among other factors. As a result of these enhancements in the communications field, wireless communications has had, and will continue to have, a significant impact on a growing number of the communicating public.
Wireless communication systems are widely deployed to provide various communication services such as voice, packet data, multi-media broadcast, text messaging, and so on. These systems may be multiple-access systems capable of supporting communication for multiple users by sharing the available system resources. Examples of such multiple-access systems include Code Division Multiple Access (CDMA) systems, Time Division Multiple Access (TDMA) systems, Frequency Division Multiple Access (FDMA) systems, and Orthogonal Frequency Division Multiple Access (OFDMA) systems. A CDMA system may implement a radio access technology (RAT) such as Wideband CDMA (W-CDMA), cdma2000, and so on. RAT refers to the technology used for over-the-air communication. W-CDMA is described in documents from a consortium named “3rd Generation Partnership Project” (3GPP). cdma2000 is described in documents from a consortium named “3rd Generation Partnership Project 2” (3GPP2). 3GPP and 3GPP2 documents are publicly available.
Communication performed within the wireless communication system may be accomplished via a unicast transmission and/or via a broadcast transmission through an Enhanced Multimedia Broadcast/Multicast Communication Service (E-MBMS) in a time division multiplex (TDM) slotted mode, for example. A unicast transmission is defined as a communication that is transmitted from one single point to another single point (e.g., from one transmitter to one receiver); whereas a broadcast transmission is defined as a communication that is transmitted from one point to multiple other points (e.g., from one transmitter to multiple receivers).
When performing channel estimation in a receiver for coherent demodulation, typically the pilots present in the one or two symbols occurring prior to and the one or two symbols occurring after the symbol being analyzed for channel estimation are also analyzed to provide for a more accurate channel estimation. Accordingly, the channel estimation is performed by averaging the analysis of the pilots over three to five symbols (i.e., the symbol under analysis and the one or two symbols preceding and one or two symbols following the symbol under analysis). However, the effective delay spread of a single frequency network (SFN) broadcast channel is much larger than a unicast channel and the required number of FDM pilot tones increases as the delay spread of the channel increases. Accordingly, because the number of pilot tones used for a broadcast transmission is much greater than the number of pilot tones used for a unicast transmission, channel estimation may be significantly degraded when a symbol from a broadcast transmission slot is adjacent to a symbol from a unicast transmission slot.
The present invention is directed to overcoming, or at least reducing the effects of, one or more problems indicated above.